1. Field Of The Invention
This invention relates to the expansion of particulate tobacco.
2. Brief Description of the Prior Art
It is an established practice in the tobacco industry to expand and/or to dry particulate tobacco by feeding the tobacco into a transport duct in which flows a hot gaseous medium, hot air and/or steam for example, whereby the tobacco is entrained in and pneumatically transported by the medium along the duct to tobacco/medium separation means. During the contact time of the tobacco with the hot gaseous medium in the transport duct, heat transfers from the medium to the tobacco particles, whereby there is effected a reduction of the moisture content of the tobacco particles. In some expansion processes the tobacco fed to the duct has been treated with an organic or inorganic expansion agent. In these processes the heat transferred to the tobacco from the gaseous medium serves to drive off the expansion agent, by evaporation or volatilisation from the tobacco.
Examples of pneumatic transport tobacco expansion processes are disclosed in United Kingdom Pat. Nos. 2,044,596A; 2,111,820A (U.S. Pat. No. 4,407,306); 2,122,321A; 2,155,302A; U.S. Pat. Nos. 3,386,773; 3,524,452; 3,575,178; 3,693,631; 4,044,780; 4,167,191; 4,418,706 and European Pat. Nos. 029 588 and 074 059 (U.S. Pat. 4,523,598.)
It is the teaching of EP 029 588 that if for the tobacco/medium separation means there is employed a tangential-type separator, there is accrued the advantage that the particle residence time of the tobacco in the separator is lower than that obtainable in the prior proposed cyclone-type separators. Certain it is that the longer the residence time within the separator the greater is the tendency for a proportion at least of the tobacco particles to be unduly dried. Another reason for the desirability of a low residence time in the separator is that a higher heat transfer efficiency occurs in the transport duct than in the separator, owing not only to the temperature differential between the tobacco particles and the hot gaseous medium in the duct but also to the velocity differential initially obtaining therebetween in the duct.
In U. S. Pat. No. 3,580,644 there is disclosed an automatic tobacco conveying system for pneumatically conveying tobacco from a storage area to a cigarette making machine. The system includes a separator comprising a casing, a gaseous-medium inlet to the casing, a gaseous-medium outlet from the casing which outlet is disposed generally opposite the gaseous-medium inlet, a gas pervious separation screen extending across the interior of the casing such that the gaseous-medium inlet and gaseous-medium outlet are at opposite sides of the screen, and a tobacco outlet at the same side of the screen as is the gaseous-medium inlet. A separator comprising these features is referred to hereinafter as a "separator as defined." A separator as defined is also disclosed in United Kingdom Pat. No. 1 575 175.
The present invention is based upon the realisation that an advantageous advance in the tobacco expansion art may be obtained by the use in a pneumatic transport tobacco expansion process of a separator as defined. Summary of the Invention
The present invention provides a method of expanding tobacco, wherein a flow of hot gaseous medium is established in a transport duct, particulate tobacco treated with an expansion agent is fed into said duct, and downstream of said duct said tobacco and said medium are separated in a separator as defined.
Cut stem tobaccos, cut lamina tobaccos or blends thereof may be treated in accordance with the present invention. The gaseous medium may be, for example, steam, air, steam and air, or nitrogen.
The expansion agent may be water, an organic expansion agent or an inorganic expansion agent, an example of the last mentioned being carbon dioxide.
The temperature of the gaseous medium at the upstream end of the transport duct may be in excess of 350.degree. C.
The present invention also provides tobacco expansion apparatus comprising gaseous medium supply means operable to supply hot gaseous medium, a transport duct, an upstream end of which duct is in gas flow communication with said supply means, tobacco feed means by which particulate tobacco can be fed to said duct, and a separator as defined, the gaseous-medium inlet of said separator being in gas flow communication with the downstream end of said duct.